The present invention relates to a control device for a vehicular engine continuously variable transmission system.
In a control method for a vehicular engine continuously variable transmission system which is proposed in the above mentioned U.S. patent application No. 362,489 now U.S. Pat. No. 4,543,077 a shift pattern for a throttle opening degree and a vehicle speed is stored, a shift command signal is obtained by retrieval based on an actual throttle opening degree and an actual vehicle speed, and a shift motor is controllably actuated based on this shift command signal so as to establish the desired reduction ratio. Although the shift motor actuates a shift control valve so as to control the distribution of oil pressure between a drive pulley cylinder chamber and a driven pulley cylinder chamber, this shift motor is so controlled as to rotate at a constant speed. This means that the rotational speed of the shift motor is unchanged regardless of the case where an accelerator pedal is depressed for acceleration and the case where the accelerator pedal is released for coasting.
However, the previously proposed control method poses the problem as follows. In order to provide a good shift response upon depressing an accelerator pedal for acceleration, it is the usual practice to set the rotational speed of the shift motor at a relatively high speed. This causes the shift motor to rotate at the same high speed when upshifting as when downshifting, resulting in an abrupt upshift. This abrupt shifting cause the driver to feel an acceleration even after releasing the accelerator pedal, making him/her feel uneasy.
In attempting to solve the problem as above, U.S. patent application Ser. No. 560,940 proposes a control method whereby the rotating speed of a shift motor is delayed in upshifting as compared to that in downshifting. This control method is adapted for an open loop control, and is not fit for a high precision closed loop control, thus failing to provide a complete solution to the above mentioned problem for the closed loop control.